Interannual Variability of Shelf and Slope Circulations in the Northern South China Sea
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Interannual Variability of Shelf and Slope Circulations in the Northern South China Sea LIU Na1), GENG Bingxu1), 2), 3), *, XUE Huijie1), 4), XIU Peng1), 2), 3), WANG Qiang1), and WANG Dongxiao1) 1) State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China 2) Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China 3) Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences, Guangzhou 510301, China 4) School of Marine Sciences, University of Maine, Orono, ME 04469-5706, USA (Received January 9, 2020; revised April 12, 2020; accepted May 12, 2020) © Ocean University of China, Science Press and Springer-Verlag GmbH Germany 2020 Abstract The northern South China Sea (NSCS) is a dynamically complex region whose shelf and slope currents are driven by different mechanisms. In this study, we used field measurements to identify clear interannual variations in the circulation related to the El Niño-Southern Oscillation cycle. To investigate the modulation mechanisms, we used a high-resolution numerical model that covers the shelf and slope regions of the NSCS. The results indicate that the stronger southwestward slope current during La Niña and stronger northeastward shelf current during El Niño in summer and winter are largely related to changes in wind forcing. The Kuroshio intrusion into the NSCS does not appear to significantly affect the circulation in the southwestern shelf region. Key words
shelf and slope circulation; ENSO cycle; ADCP measurements; numerical simulation
1 Introduction The South China Sea (SCS) is the largest semi-enclosed marginal sea of the northwestern Pacific. Its upper-layer circulation is driven mainly by monsoon winds. In winter, a basin-wide cyclonic gyre is established, and in summer the circulation splits into a weakened cyclonic gyre north of approximately 12˚N and a strong anticyclonic gyre to the south (Qu, 2000; Su, 2004). The SCS is also influenced by external fluxes from the adjacent open ocean. The SCS is connected with the East China Sea through the Taiwan Strait, with the Pacific Ocean through the Luzon Strait, and with the Java Sea through the Karimata Strait. The continental shelves are wide in the northern and southwestern SCS, but extremely narrow in the east and west. The continental shelf in the northern SCS is about 150–250 km wide, with the Dongsha Islands located about 200 km offshore on a plateau over the upper continental slope. There are generally three major band-like currents in the northern SCS (NSCS), namely the Guangdong coastal current, the South China Sea Warm Current (SCSWC), and the slope current (Fig.1; Huang et al., 1992; Guan, 1998; Su, 2004; Shu et al., 2018). The Guangdong coastal * Corresponding author. E-mail: [email protected]
current has two branches. The branch to the west of the Pearl River Estuary is relatively stable and flows westward year-round (Zhong, 1990; Wu, 1990; Bao et
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